Plastic is a versatile material that can be rotationally cast, injection moulded, heated and vacuum or pressure formed and even draped over form-work to make a variety of shapes for various purposes. For mass production, injection moulding is a preferred method because it is fast, energy efficient and gives more precision of shape and size. It is, however, limiting in that internal cavities can't be made without welding or gluing the components together. For some plastics, especially those in the polyolefin group like the very popular polypropylene, gluing is not normally successful, so welding or using mechanical compression fittings and seals is the only real joining alternative. Compression fittings are limited in how big they can be in practice because of expense. They are also predominantly used for standard sized pipe as making compression fittings for the variety of shapes required for consumer items is not practical. Even if it were practical for small items, moulded compression fittings are not practical nor cost effective for large plastic pails, so in these circumstances fabrication and welding is the only realistic alternative.
Several methods of welding are practiced. Butt welding involves cutting and cleaning both surfaces to be joined and then heating them before they are pushed together while still molten. This type of joint can leave an internal weld bead which is difficult to remove and can cause ragging that could lead to blockages when used for sewer pipelines. Fusion welding, where fittings have electrical resistance wire built into the components to melt the plastic, is also popular. Fusion joints can be pushed together whilst clean, then electrical energy is used to heat the bonding surfaces of the joint to fuse the parts together and so achieve a good seal. Other forms of welding include ultrasonic and hot air welding and both are time consuming and require specialist equipment and skills to bond joints successfully and safely. All forms of welding can produce toxic fumes and require good ventilation or breathing apparatus to be worn.
This significantly limits the uses to which plastics could otherwise be put, because it is time consuming and expensive to fabricate good quality joints on large components. Also, getting smooth curves when cold bending plastics for fabricated components is problematic and so is seldom done commercially.
Drums and pails are commonly used for the storage of hazardous or messy liquids and powders. They must have positive seals that are robust, even when dropped. Commonly used bucket type clips are prone to leakage, have a limited shelf life and once opened are no longer very effective. Threads provide a positive joining method but are expensive to mould, especially on large plastic components, and if they become too large they are very difficult to undo or tighten in real world conditions. Threads also are limited to use on circular joint face profiles with planar joint faces.
The present inventors have now developed a general connecting method for connecting two or more components together which may be made of plastics material or of any other suitable type of material. Described herein are further improvements in the connecting mechanism described in the specifications of U.S. application Ser. No. 12/636,259, International Patent Application No. PCT/AU2008/000839 and International Patent Application No. PCT/AU2010/000240 In one or more embodiments the connecting mechanism minimises or overcomes one or more of the component-joining problems referred to above.